This invention relates to an axial thrust balancing system suitable for use with a multi-stage centrifugal pump, multi-stage centrifugal compressor, etc.
One type of axial thrust balancing system known in the art comprises a sleeve mounted on a rotary shaft for balancing axial thrust, a bush separated from the sleeve by a small annular clearance, a high pressure balance chamber interposed between the sleeve and the back of an impeller, and a low pressure balance chamber located on a side of the sleeve opposite the side on which an impeller is located.
In this construction, the majority of the fluid drawn by suction through a suction port of the impeller and discharged from the impeller through a discharge port is supplied through an outlet casing to a predetermined position. Part of the discharge fluid flows into the high pressure balancing chamber located behind the impeller and through the clearance and the low pressure balance chamber to be led to the suction side of a pump or released to the atmosphere.
In the aforesaid axial thrust balancing system, the discharge pressure and the suction pressure of the pump act, for example, on side walls of the sleeve adjacent the high pressure balance chamber and low pressure balance chamber, so that the axial thrust acting in the direction of the suction port of the impeller can be mitigated by the sleeve.
In the aforesaid construction, a fluid filled in the clearance in the form of a thin film performs a sort of bearing function like a film of lubricant formed on a journal bearing. When the rotary shaft is rotated at an angular velocity which is higher than the natural angular frequency of the shafting, self-excited vibration of the shaft may occur as similar to the oil whip of the lubricated-journal bearing.